Circulation and Cardiovascular Systems Notes
32.2 Transport in Vertebrates
All vertebrates have a closed circulatory system called a cardiovascular system.
Vertebrate heart:
Atria receive blood from general circulation.
Ventricles pump blood out through blood vessels.
Vertebrate vessels:
Arteries carry blood away from the heart.
Arterioles are small arteries leading to capillaries.
Their diameters are regulated by the nervous and endocrine systems.
Capillaries exchange materials with tissue fluid (interstitial).
Venules join to form a vein.
Veins return blood to the heart.
Both venules and veins collect blood from capillary beds.
Comparison of Circulatory Pathways
Fish: Blood flows in a single loop.
Single atrium and single ventricle.
Amphibians: Blood flows in a double loop.
Systemic circuit and pulmonary circuit.
Two atria with a single ventricle.
Most reptiles: A septum partially divides the ventricle.
Mixing of oxygen-rich and oxygen-poor blood is kept to a minimum.
In crocodilians, the septum completely separates the ventricle.
Birds and mammals: Blood flows in a double loop (two circuits).
The heart is also divided by a septum into separate sides.
The right ventricle pumps blood to the lungs; the left ventricle pumps blood to the rest of the body.
Blood pressure is adequate for both pulmonary and systemic circuits.
32.3 The Human Cardiovascular System
The Human Heart:
Fist-sized and cone-shaped.
Located between the lungs directly behind the sternum (breastbone).
Muscular organ (cardiac fibers).
Lies within a membranous sac (the pericardium).
Structure of the Heart:
The septum separates the heart into left and right sides.
Each side has two chambers:
Atria (upper chambers):
Thin-walled.
Receive blood from circulation.
Ventricles (lower chambers):
Thick-walled.
Pump blood away from the heart.
Valves:
Valves open and close to control blood flow through the heart.
Atrioventricular valves:
Tricuspid valve: between the right atrium and ventricle.
Bicuspid valve: between the left atrium and ventricle.
Semilunar valves:
Pulmonary semilunar valve: between the right ventricle and pulmonary trunk.
Aortic semilunar valve: between the left ventricle and aorta.
Pathway of Blood Through Heart:
Blood returning to the heart from the systemic circuit:
Venae cavae return blood to the right atrium.
The right atrium pumps blood through the tricuspid valve to the right ventricle.
The right ventricle pumps blood through the pulmonary semilunar valve to the pulmonary circuit.
Blood returning to the heart from the pulmonary circuit:
Enters the left atrium.
The left atrium pumps blood through the bicuspid valve to the left ventricle.
The left ventricle pumps blood through the aortic semilunar valve to the systemic circuit.
Oxygen-poor blood never mixes with oxygen-rich blood (in humans).
Blood must go through the lungs in order to pass from the right side to the left side of the heart.
Heartbeat:
Systole: Contraction of heart chambers.
Diastole: Relaxation of heart chambers.
Cardiac cycle: Two-part pumping action that takes about a second.
Blood collects in the atria; the atria contract, pushing blood through the tricuspid and mitral valves into the resting lower ventricles. This phase (the longer of the two) is called diastole.
The second part begins after the ventricles fill; the ventricles contract. Is phase is called systole. After blood moves into the pulmonary artery and aorta, the ventricles relax.
Pulse and Conduction System:
The pulse is a wave effect passing down the walls of the arterial blood vessels when the aorta expands and recoils following ventricular systole.
Rhythmic contraction of the atria and ventricles is due to the internal (intrinsic) conduction system of the heart.
Sinoatrial node (SA) keeps the heartbeat regular and is called the pacemaker.
Atrioventricular node (AV) signals ventricles to contract.
Input from the brain can increase or decrease the rate/strength of heart contractions.
The hormones epinephrine and norepinephrine, secreted into the blood by the adrenal glands, also stimulate the heart.
Electrocardiogram (ECG):
A recording of electrical changes that occur in the myocardium during the cardiac cycle.
When the SA node triggers an impulse, the atrial fibers produce an electrical charge (P wave).
The P wave indicates that the atria are about to contract.
The QRS complex signals that the ventricles are about to contract and the atria are relaxing.
The T wave is due to electrical changes occurring as the ventricular muscle fibers recover.
Comparison of Circulatory Circuits:
Pulmonary Circuit:
Takes O2-poor blood to the lungs, returning O2-rich blood to the heart.
Systemic Circuit:
Takes O2-rich blood from the heart to tissues throughout the body, returning O2-poor blood to the heart through the venae cavae.
Portal System:
In a portal system, blood from capillaries goes through veins to another set of capillaries without traveling first through the heart.
Example: the hepatic portal system takes blood from the intestines directly to the liver.
Blood Pressure:
Contraction of the heart supplies pressure that keeps blood moving in the arteries.
Systolic pressure results from blood forced into the arteries during ventricular systole.
Diastolic pressure is the pressure in the arteries during ventricular diastole.
Normally measured with a sphygmomanometer on the brachial artery, an artery on the upper arm.
Expressed in the form: Systolic “over” Diastolic (e.g., 120/80).
Blood pressure is measured in millimeters (mm) of mercury.
Mechanics of Blood Pressure:
In arteries, the pressure of the blood forces it to move forward.
Blood pressure falls as blood flows from the aorta into arteries and arterioles.
Blood flow in the capillaries is slow.
Blood pressure in the veins is too low to move blood back to the heart.
Skeletal muscle contraction pushes blood in the veins toward the heart.
Veins have valves to prevent backward flow of blood.
Varicose veins develop when valves become ineffective.
A respiratory pump reduces pressure in the thoracic cavity to cause blood to move from the abdominal cavity (higher pressure) into the thoracic cavity (lower pressure) during each inhalation.
Cardiovascular Disease (CVD):
Leading cause of death in most Western countries.
Hypertension: High blood pressure.
30% of Americans are sufferers.
Caused by narrowing of arteries due to atherosclerosis.
Atherosclerosis: Accumulation of fatty materials between the inner linings of arteries.
Deposits are called plaque.
A clot, called a thrombus, may form on an arterial wall.
Stroke: A disruption of blood supply to the brain.
Results when a cranial arteriole bursts or is blocked by an embolus.
Angina pectoris: Painful squeezing sensation from myocardial oxygen insufficiency due to partial blockage of a coronary artery.
Heart attack (myocardial infarction): Coronary artery becomes completely blocked.
Stents, or self-expanding wire mesh tubes, can be inserted into a blocked artery to keep it open.
If stents are unsuccessful, a coronary bypass may be required in which a surgeon replaces the artery with a healthy artery from elsewhere in the body.
32.4 Blood
Functions of Blood:
Transports gases, nutrients, waste products, antibodies, and hormones throughout the body.
Helps combat pathogenic microorganisms.
Helps maintain water balance and pH.
Regulates body temperature.
Carries platelets and factors that ensure clotting to prevent blood loss.
Composition of Blood:
Plasma (liquid portion):
Water (90-92% of plasma): Maintains blood volume, transports molecules.
Plasma proteins (7-8% of plasma):
Albumins: Maintain blood osmotic pressure and pH.
Globulins: Transport; fight infection
Fibrinogen: Blood clotting.
Salts (less than 1% of plasma): Maintain blood osmotic pressure and pH; aid metabolism.
Gases (O2 and CO2): Cellular respiration.
Nutrients (lipids, glucose, and amino acids): Food for cells.
Wastes (urea and uric acid): End product of metabolism; excretion by kidneys
Hormones: Aid metabolism.
Formed Elements (cells and cell fragments):
Red blood cells (erythrocytes): Transport O2 and help transport CO2. 4 million to 6 million per cubic millimeter of blood.
White blood cells (leukocytes): Fight infection. 5,000 to 11,000 per cubic millimeter of blood.
Neutrophils: 40-70%
Lymphocytes: 20-45%
Monocytes: 4-8%
Eosinophils: 1-4%
Basophils: 0-1%
Platelets (thrombocytes): Aid clotting. 150,000 to 300,000 per cubic millimeter of blood.
Red Blood Cells (RBCs):
Small, biconcave disks.
Lack a nucleus and contain hemoglobin.
Hemoglobin contains:
Four globin protein chains.
Each associated with heme, an iron-containing group.
Manufactured continuously in bone marrow of the skull, ribs, vertebrae, and ends of long bones.
If the number of RBCs is insufficient or if cells don’t have enough hemoglobin, the individual has anemia.
The hormone, erythropoietin, stimulates RBC production.
Blood Types:
Blood type is determined by the presence or absence of a surface antigen.
ABO System.
Rh System.
Antibodies in the plasma can cause agglutination.
Cross-reactions occur when antigens meet antibodies.
Organ damage can result.
ABO System:
Blood Type A:
Antigen on Red Blood Cells: A
Antibody in Plasma: Anti-B
Blood Type B:
Antigen on Red Blood Cells: B
Antibody in Plasma: Anti-A
Blood Type AB:
Antigen on Red Blood Cells: A, B
Antibody in Plasma: None
Blood Type O:
Antigen on Red Blood Cells: None
Antibody in Plasma: Anti-A and anti-B
Rh System:
During pregnancy, if the mother is Rh negative and the father is Rh positive, the child may be Rh positive.
Rh-positive red blood cells may leak across the placenta, and the mother will produce anti-Rh antibodies.
Hemolytic disease of the newborn (HDN) occurs when anti-Rh antibodies cross the placenta and attack the RBCs of another Rh-positive baby in a subsequent pregnancy.
HDN can be prevented by giving an Rh-negative woman an Rh immunoglobulin injection within 72 hours of bearing an Rh-positive child.
White Blood Cells (WBCs):
Most types are larger than red blood cells.
Contain a nucleus and lack hemoglobin.
Important in the inflammatory response.
Divided into two categories based on the presence or absence of cytoplasmic granules:
Granular leukocytes:
Neutrophils, eosinophils, and basophils.
Agranular leukocytes:
Monocytes and lymphocytes.
Granular Leukocytes:
Contain granules composed of proteins and enzymes used to help defend the body against invading organisms.
Neutrophils: Phagocytize and digest bacteria.
Basophil: Contains histamine.
Eosinophils: Involved in fighting parasitic worms, among other activities.
Agranular Leukocytes:
Lack granules.
Monocytes: Migrate into tissues in response to chronic, ongoing infections.
Differentiate into macrophages.
Fight infection, release growth factors that increase the production of WBCs by the bone marrow.
Lymphocytes:
T cells and B cells involved in the immune response and antibody production.
Platelets:
Result from fragmentation of megakaryocytes in red bone marrow.
Non-cellular, formed elements.
150,000 to 300,000 per cubic millimeter of blood.
Involved in blood clotting (coagulation).
A blood clot consists of:
Platelets.
Red blood cells.
Fibrin threads.
Thrombin is an enzyme that, when activated by prothrombin activator, converts fibrinogen to fibrin.
Fibrin threads wind around the platelet plug to provide a framework for a clot.
Plasmin destroys the fibrin network.
Capillary Exchange:
Capillaries are very narrow, and tiny RBCs must go through single file.
The movement of fluid through a capillary wall is controlled by osmotic pressure and blood pressure.
Walls of capillaries are very thin to facilitate diffusion of nutrients, gases, and wastes.
Water exits a capillary near the arterial end.
Water enters a capillary near the venous end.
Solutes diffuse into and out of a capillary according to their concentration gradient.
Oxygen and nutrients diffuse out of capillaries.
Carbon dioxide and wastes diffuse into the capillary.
Capillary Exchange and Lymph:
Substances leaving capillaries contribute to interstitial fluid.
Excess interstitial fluid is collected by lymphatic capillaries and is called lymph.
Lymph is returned to systemic venous blood when the major lymphatic vessels enter the subclavian veins in the shoulder region.